We are concerned with seveal problems in virus structure that exemplify important kinds of macromolecular interaction. During the coming year, we hope to obtain a 2.8 Angstrom resolution electron density map of tomato bushy stunt virus from single-crystal X-ray diffraction data currently being measured. This should enable us to build an atomic-resolution model and to visualize thereby details of protein RNA interactions. In addition, we proposed to extend studies on bacteriophage morphogenesis to include a more detailed three-dimensional investigation of phage P22 and its prohead by electron microscopy (together with 3-D image reconstruction, and by attempted crystallization of proheads. Attempts will also be made to obtain two-dimensionally crystalline arrays of Sindbis virus glycoprotein suitable for detailed analysis of electron microscopy. BIBLIOGRAPHIC REFERENCES: Earnshaw, W., Casjens, S. and Harrison, S.C. "X-ray Diffraction from P22 Heads" J. Mol. Biol. (1976) 104, 387-410. Harrison, S.C. and Kornberg, R.D. "X-ray Diffraction from Isolated Repeat Units of Chromatin", in Molecular Mechanisms in the Control of Gene Expression (Academic Press, 1976).